Method of improving the insulation of vacuum tubes



Oct. 19 1926.

R. JAEGER METHOD OF IMPROYING THE INSULATION 0F VACUUM TUBES Filed Oct. 19, 1922 Patented Oct. 19, 1926.

UNITED- STATES PATENT OFFICE.

ROBERT JAEGER, OF BERLIN-FRIEDENAU, GERMANY, ASSIGNOR TO SIEMENS & HALSKI.,'AKTIENGESELLSCI-IAIET` OF SIEMENSSTADT, NEAR BERLIN, GERMANY, A

CORPORATION OF GERMANY.

METHOD OF IMPROVING THE INSULATION OF VACUUM TUBES.

Application led October 1,9, 1922, Serial No. 595,602, and in Germany -October 29, 1821.

surface resistance between grid and, for in.

stance, cathode.

Now, it could be attempted to improve the surface insulation by coating the outer surface of the tube with bakelite, as is, fory instance, done with the ebonite parts of electrical machines.

This insulation is, however, not suiciently effective for the purpose 1n--question, as it cannot be avoided, when using the tubes, that. the. bakelite layer is touched by the hands and thus a conductive layer will still be produced on the bakelite coating through a direct transmission by the han s.

.The present invention overcomes this drawback by displacing at least part of the electric leakage path at the outer surface into a cavity, of which the walls are highly insulated by an appropriate coating, for instance of bakelite, and freed from the mois'- ture lm, said cavity being, moreover, closed by a non-hygroscopic insulator of high value, for instance of amber.

The accompanying drawing shows two appropriate constructional forms of the sub'ect matter of the present invention:

Big. 1 is a side elevation, partly in section, of one form, while F1g. 2 is a fragmentary sectional elevation, of the other form.

' Referring to Fig. 1: 1 designates a gridtube, in the upper end of which the lead d to the control-grid s is molten-in at e, while the lead to the other electrodes at the lower end of the grid-tube is effected in a way known in the art.` B this arrangement, a far outer electric lea age path is ensured between the electrode of the control-grid and the other electrodes. At its upper end, the grid-tube r carries a tubular extension r1, which is closed at its outer end by an 'amber piece b. In the middle of the latter a connection-terminal lc for the lead d to the controlrid s is provided. The inner 'surface of e tubular extension 'r1 may be provided with a lacquer coating 'i of a phenol resin condensation product, as shown.

The tubular extension 1*, has a lateral branch 12, on which a glass container g with a drying mediumtherein, for instance phosphor pentoxide, is arranged by means of screwed brass rlngs fm,1 and m2.

By the improved arrangement, rst, the electric leakage path from the electrodes at the lower end of the grid tube 1' to the molten-in point e of the lead d to the control-grid s, is extended through the inner surface of the tubular projection r1. Apart from this extension, however, the important fact may be added that the inner surface of the tubular extension r, maybe highly insulated, e. g. by a lacquer of bakelite and said insulation is so arranged that it cannot be attacked by outer influences.

With the employment of the insulating amber piece b closing said insulated cavity, the insulating capaclty isconsiderably increased, while the moisture labsorbing medium in the glass container g prevents any moisture, which might still penetrate through the joining of the amber piece b to the tubu lar extension r1, settling 'on the bakelite coating.

Referring to Fig. 2: The wall of the gridtube r has a re-entrant portion in such a way that a ring p is formed therein, the inner surface of said re-entrant portion being coated with a lacquer of bakelite and its annular open end closed by means of an amber col ar b1.

One or a plurality of such re-entrant portions with highly insulated surface may be sutiicient without the employment of an amber collar as long as the insulated surfaes cannot be .directly touched from outsi e.

A safety against moisture in the interior of the cavities r1, or p respectively, can also be attained by maklng the latter airtight and evacuating the same.

The insulating cavities may also be em- 4 tric leakage path between the electrodes to be insulated from each other in an outwardly o ning cavity, the walls of'which consistof te same material as the tube, and in lclosing the outwardr opening of said cavity by means of a non-hygroscopic insulator, whose insulating resistance is considerably higher than that of the tube material.

2. A method of improving the insulation at the outer surface of vacuum tubes, particularly of vacuum tube voltmeters, comprising arranging at least part of the outer electric leakage ath between the electrodes to be insulated rom each other in an outward.

`ly opening cavity, closing the opening of said cavity by means of an insulator of high value, and locating a drying agent in said cavity. f

3. A method of im roving the insulation at the outer surface o vacuum tubes, particularly of vacuum tube voltmeters, comprising arranging at least part ofthe outer electric leakage ath between the electrodes to be insulated rom each other in an outwardly opening cavity, closing the openin of said cavit v by means of an insulator of igh value, an evacuating said cavity.

4. A. method of im roving the insulation at the outer surface o vacuum tubes, particularly of vacuum tube voltmeters, comprising arranging at least part of the outer electric leakage ath between the electrodes to be insulated rom each other inan outwardly opening cavity, closing the opening of said cavity by means of an insulator of high value, and highly insulating the walls of said cavity.

-the electrodes to be insulated, and a cover of amber adapted to close the opening of said recess and a drying medium of the character of powdered phosphorpentoxide (P205) disposed-in said recess.'

7. Arrangement for improving the `insula tion at the outer surface of vacuum glasstubes, particularly of vacuum tube voltmeters,. comprising a re-entrant wall portion of glass forming an outwardly opening recess at the tube interposed into at least part. of the outer electric leakage path between the electrodes to be insulated, a cover of non-hygroscopic insulating material of thecharacter of amber adapted to close the opening of said recess, powdered phosphorpentoxide (P205), disposed in said rece and a phenol resinous lacquer coating covering the inner surface of the walls of said recess.

8. A method of im roving the insulation at the outer surface o vacuum tubes, partican outwardly open ularly of vacuum tube voltmeters, comprising arranging at least part of the outer electric leakage path between the electrodes to be insulatedfrom each other in an outwardly opening cavity, whose walls consist of the same materiall as the tube, and in closin the outer opening of said cavity by means o a non-hygroscopic insulator, whose insulating resistance is of the character of that of amber.

l lIn testimony whereof I affix my signature.

ROBERT JAEGER. 

